This invention relates generally to improved membrane filter type artificial hollow fibers whose filtering tubular walls are formed therein a three-dimensional net-like system of fine filtering passages. The invention relates further to a process for the manufacture of such hollow fibers.
Hollow fibers having the reverse osmotic membrane performance of substantially unified structure have hitherto been known, as revealed in Japanese Patent Publication Nos. Sho-44-14215 and Sho-49-34305, published June 24, 1969 and Sept. 13, 1974, respectively, in the name of The Dow Chemical Corporation, Mich.
Other reverse osmotic hollow-fibers as proposed in Japanese Opened Patent Specification Nos. Sho-47-4010 and Sho-49-50289, opened to public inspection Feb. 28, 1972 and May 15, 1974, respectively, in the name of Monsanto Company, Mo., comprise a most dense, highly thin layer or active one locally positioned rather in close proximity to either wall surface of the fiber, characterized by gradually larger pore sizes with viewed in section thereof and towards the inside wall surface of the fiber.
Ultra filtration hollow fibers are also known as revealed in Japanese Patent Publication No. Sho-47-40890 and Japanese Opened Patent Specification No. Sho-49-90684, published Oct. 16, 1972 and opened Aug. 29, 1974 to public inspection, respectively and in the respective name of Rhone-Poulenc S. A., Paris and Asahi Chemical Industry Co., Ltd., Osaka. These hollow fibers have its active layer formed on either outer or inner wall surface of the fiber.
It should be mentioned that the above former type hollow fibers represent only reverse osmotic membrane performance, thereby the pore size being all less than 0.001.mu.. Therefore, their practical use was directed in the dialysis with artificial kidneys and the salt separation from sea water and similar jobs. Generally speaking, these hollow fibers are exclusively used for filtering separation of highly fine ingredients.
On the contrary, the above latter type hollow fibers for ultra filtration are effectively utilized for filtering separation of those which have similar molecular weights to urea, vitamine B.sub.12 and the like. This type hollow fibers have been utilized for most purposes, and indeed, with combination of the reverse osmotic hollow fibers in the refining of liquids and for separation of above products therefrom.
Specific hollow fibers are also known as revealed in Japanese Open Patent Specification No. Sho-48-77111 opened Oct. 17, 1973 in the name of Asahi Chemical Industry Co., Ltd., Osaka, representing finer pore passages than 10.mu.. According to our precise experiments, however, substantial difficulties have been experienced in the realization of unified structure of whole tubular wall which represents gradually finer pore passages when seen in cross-section towards the inside wall surface.
It is, therefore, a main object of the present invention to provide a hollow fiber having the membrane filtration performance according to which yeasts, fungi, pathologenic viruses and the like may advantageously be retained during filtration, while urease, albumin, haemoglobin and the like may pass through the pore passages of the hollow fiber, thus providing a unique and specific filter performance which can not be attained in the past by use of the hollow fiber.
A further object is to provide a highly improved hollow fiber providing the reversible filtering performance through the pored fiber wall with substantially equal results, thus representing a substantially broadened availability of the hollow fiber liquid filter.